Electrolytic condenser



- Aug. 11, 1936. s; R B'EN 2,050,587

ELECTROLYTI C CONDENSER Filed Feb. 17, 1934 INVENTOR Samuel ifazm ATTORNEY Patented Aug. 11, 1936 STATES PATENT'OFFICE ELECTROLYTIC CQNEENSER Samuel Ruben, New Rochelle, N. Y., assimor to Ruben Condenser Company, Dover, IBeL, a corporation of Delaware Application February i7, 319%, Serial No. 711,629

8 Claims. (Cl. 115-315) This invention relates to electrolytic condensers. with the frequency. The oxide film loss increases Specifically, it relates to electrolytic condensers with thickness of the oxide layer for a given oi the dry type and film forming electrodes suitvoltage. and also with temperature. able for use therein. Initially, the thickness of the oxide is deter- An object of the invention is to provide an mined in a given electrolyte, by the applied film 5 electrolytic condenser having an electrode which forming potential. I believe that the subsequent forms a dielectric film more readily than conincrease in film thickness is due to leakage denser electrodes of the prior art and which genthrough the film, due in turn to porosity. This erally has improved film forming properties. efiect is aggravated at higher temperatures.

10 A further object is to provide an electrolytic In the present invention,'I utilize an electrode 10 condenser electrode having a greater capacity formed from an alloy of aluminum and tantalum. per unit area than electrodes of the prior art. I have found that the film formed from such an Another object of the invention is to provide electrode has a greater capacitance per unit area, an aluminum-tantalum electrode specifically lor is much denser, has a lower leakage and for a electrolytic condensers. given electrolyte, a. lower power factor with re- 15 A further object is to provide an electrolytic duced film forming hysteresis loss, than a film capacitor capableof withstanding higher voltages formed from substantially pure aluminum. I and currents than capacitors of this type now in also find that it is capable of withstanding a use. higher temperature and of maintaining its initial Another object is to provide an electrolytic capacitance and power factor overalongenperiod. 20 capacitor-having a. very low power factor. These qualities are of particular advantage in Other objects will be apparent from the dis- -.relation to dry electrolytic condensers. which closure and from the drawing in which are now being extensively used with condenser- Fig. l is a perspective view, partly broken away, starting" motors. of one embodiment of the invention showing a The aluminum-tantalum electrode forms up fiat plate condenser; more quickly and deforms less readily, than the Fig. 2 is an end view of a modification showing aluminum electrodes. The presence of the tanan arrangement of the invention in coiled form; talum serves to minimize the possibility of corro- Fig. 3 is a vertical sectional view of an arrangesion and reduces the sensitivity to halogen salts. I merit somewhat similar to Fig. 2, enclosed within Where condensers employing a formed tan- 30 a protective casing; talum-aluminum anode are used on direct our- Fig. 4 is a cross section of another type of conrent such as in radio receivers, I find that they struction, and will withstand a much higher voltage than con- Fig. 5 is a perspective view of the device illusdensers of the prior art. For instance, in com- 5 trated in Fig. 4. parison with a condenser having an aluminum This application may be said to be a continua-- anode formed under the same conditions, a contion in part of my co-pending application S. N. denser having an anode composed of 99.9% alu- 686,887, filed 26th August 1933. minum and .1% tantalum withstood a 20% higher Heretofore, aluminum has been generally used voltage for a given leakage value. as the anode material for electrolytic condensers. The decrease in power factor of condensers 40 This is due to its desirable mechanical properties, which obtains from the use of the aluminumits low cost, and eiiective film forming charactantalum electrode may be illustrated in the folteristics. lowing typical results. The electrodes compared While generally of service, the film of oxide were of identical dimensions and wereidentically. formed on aluminum has been to a certain extent treated and formed. 45

porous, and it has a tendency to thicken with use. The efiectiveness of an electrolytic capacitor or condenser is determined by its capacitance per Electrode material 122%: unit area, leakage and power factor. The power factor of a condenser is related to such characteristics as internal resistance of electrolyte, con- 131;.) $1 131 7 T m 4 denser leakage and resistance of the dielectric a 101m 0 8 film. On alternating current, another factor is 99399; 011% [on introduced, which may be termed the electro- Percent 50 5.

n Chemical film mi ysteresis which increases The capacitance of the film-termed aluminum tantalum electrodes was also in excess of that o! the pure aluminum electrode.

- The increase in voltage breakdown and capacitance per unit area indicates the formation of a more effective, yet thinner film, on the aluminumtantalum electrode.

The percentage of tantalum to be alloyed with the aluminum depends upon the use to which the condenser is to be applied and the desired thickness of the foil. Where the foil is to be quite thin, apercentage of .05 to 1% tantalum is desirable. If more tantalum is added, rolling becomes difllcult, although for some purposes it may be of advantage to increase the percentage oitantalum to 2%. For present day requirements, I do not believe it necessary to increase the tantalum content substantially above the latter percentage.

. method. I prefer to use. a solution of chemically pure sodium hereto and boric acid in distilled water for the forming bath. The cooperating electrode should preferably be made from the some metal and if the condenser is to be used for alternating current work, it should be similarly film-formed. It has been found that the forming time for an aluminum tantalum alloy electrode is less than one half of that required to form an electrode of pine aluminum, in the same solution.

I prefer to use the electrode of this invention in condensers of the dry electrolytic type as described in my Patents K 1310,0173;

' 1,891,207; 1918,7116, etc.

It will be seen from a reading of these patents that the condensers can be constructed with a fibrous porous spacer such as gauze or with a non-fibrous spacer such as sheet cellulose. I

prefer to use the type of spacer and electrolyte described in my Patent 1,918,716. Preferably, I use a regenerated non-fibrous cellulose sheet such as embossed cellophane which has been conductively plasticized by ersion in an adhesive film maintaining electrolyte, which may be made as follows:

859 grams of boric acid, 20b cc. of 28% ammoni hydroxide and 640) cc. of ethylene glycol are stirred and heated to 128 C. and kept at approximately that temperature for about ten minutes. To three parts of this paste I add by weight, one part or a mixture made as follows: Two parts of pure gelatine powder are dissolved in two parts water to which is added three parts of ethylene glycol. The mixture is stirred and heated to lot C. to allow free water to be evaporated. The combined mixture consisting of 75% of the glycol-boric acid-ammonia and 25% gelatinized glycol is then heamd to 128 C. The resulting product is an adhesive mixture which sticks tenaciously to the electrodes and the spacer and which becomes absorbed into and permeates the spacer. When heated, it does not tend to leave the plates or collect into circular areas. This quality is of fundamental importance in connection with condensers which employ the combination oi non-fibrous non-porous sheet spacers and flat foil electrodes.

. insulator .(l)

a higher resistance, electrolyte is necessary and for such conditions, I prefer to substitute pure dextrin in the order of 7% for the gelatine, or to dispense with the adhesive altogether.

In some cases, it may be desirable to use as a spacer material, cellophane which has not been thoroughly dried and which contains ammonium borate or boric acid in suspension.

One form of condenser can be constructed as follows: Two electrode sheets are coated with the gelatinized glycol-boric acid-ammonia. mixture, the conditioned embossed cellophane being placed in between the electrodes and the whole compressed to insure good physical contact. The adhesive glycol-boric acid-ammonia becomes absorbed into and suspended in the cellophane which is thereby rendered completely conductive throughout its entire surface. If the condenser is to be rolled, another cellophane spacer is used and the rolling carried out in the usual manner. Such a condenser has a, very uniform distribution of current over the entire contacting area and localization is prevented.

In order to afford a detailed description of some forms of the invention, reference is made to the accompanying drawing (in which like numbers indicate like parts).

In the flat type condenser of Fig. 1, the anode (l) composed of an aluminum-tantalum alloy having a'pre-formed oxide film or layer, is-spaced from aluminum-tantalum cathode (2) by embossed cellophane" sheet (3) which has been rendered electrolytically conductive and adhesive by the absorption of a gelatinized glycol-boric acid-ammonia compound.

In the rolled condenser of Fig. 2, an additional conductive cellophane spacer (3a) has been provided.

In the housed condenser of Fig. 3, the can t) acts as one terminal being insulated from the other terminal (t) by insulator member (5). In-

sulation at the bottom of the can is provided by (9) which serves as a protective wrapper and has its ends spun over after the condenser has been assembled. Insulator bobbins it) and (i serve as sealing means. Connections to an ternal circuit are made with terminals i2 and The unit is preferably mounted vertically to allow a circulation of air through the center electrode tube.

' It, will be seen that this construction not only obviates the necessity of providing a can but also provides a desirable construction for cool operation and mounting.

I While this application is drawn specifically to the use of an aluminum-tantalum alloy for the film forming electrode material, it is possible to form the alloy of aluminum and columbium, which, by nature, is commonly associated with tantalum as an impurity, As the latter is comparatively rare and more expensive, I prefer use tantalum as the alloying element.

In order to avoid difierences in The aluminum used in the alloy should be of the purest commercial grade obtainable, it being understood that the presence of minute impurities is practically unavoidable.

Since certain changes in carrying out the construction of the condensers and its components and obvious substitutions can be made in the materials used without departing from the scope of the invention, it is intended that all matters contained in the above description, or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. An electrode for electrolytic condensers comprising an alloy of aluminum and one of the ale ments tantalum and columbium, thepercentage of aluminum being substantially not less than 98%.

2. An electrode for electrolytic condensers comprising an alloy consisting preponderantly of aluminum and containing substantially not more than two (2%) per cent of one of the elements, tantalum and columbium.

3. An electrode for electrolytic condensers comprising an alloy consisting preponderantly of aluminum and containing substantially not more than two (2%) per cent of tantalum.

4. An electrode for electrolytic condensers comprising an alloy consisting preponderantly of aluminum. and containing substantially not more than one (1%) per cent of tantalum.

5. An electrode for electrolytic condensers comprising essentially aluminum and tantalum, the percentage of aluminum being not less than ninety-nine (99%) per cent.

6. An electrode for electrolytic condensers comprising an alloy containing as an essential ingredient thereof an element selected from group consisting of tantalum and columbium in a proportion of substantially not more than two per cent and the remainder substantially all aluminum.

'I. An electrolytic condenser comprising a container, a film-forming electrode and an electrolyte therein, said electrode being Iormed of an alloy consisting preponderantly of aluminum and containing as an essential ingredient thereof an element selected from the group consisting of tantalum and columbium in a proportion of substantially not more than two per cent.

8. A dry electrolytic condenser comprising a container and a condenser section therein, said section comprising a pair of closely spaced electrode foils at least one of which is film-formed, a flhn-maintaining electrolyte therebetween and terminals connected to said electrode foils, at least one of said electrode foils being formed of an alloy consisting preponderantly of aluminum and con taining as an essential ingredient thereof an element selected from the group consisting of tantalum and columbium in a proportion substantially not more than two per cent.

- SAMUEL RUBEN. 

